C# WinForm 检测文件是否被占用

#region 检测文件状态及操作方式选择
[DllImport("kernel32.dll")]
private static extern IntPtr _lopen(string lpPathName, int iReadWrite);
[DllImport("kernel32.dll")]
private static extern bool CloseHandle(IntPtr hObject);
private const int OF_READWRITE = 2;
private const int OF_SHARE_DENY_NONE = 0x40;
private static readonly IntPtr HFILE_ERROR = new IntPtr(-1);
/// 

/// 检测文件是否只读或被使用
/// 
/// 要检测的文件
/// true可用，false在用或只读
public static bool CheckFilesState(string fileName)
{
    if (!File.Exists(fileName))
        return true;//文件不存在
    if ((File.GetAttributes(fileName) & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)
        return false;       //文件只读
    IntPtr vHandle = _lopen(fileName, OF_READWRITE | OF_SHARE_DENY_NONE);
    if (vHandle == HFILE_ERROR)
        return false;       //文件被占用
    CloseHandle(vHandle);   //文件没被占用
    return true;
}
/// 

/// 检测文件是否只读或被使用，并由用户选择是否继续操作
/// 
/// 要检测的文件
/// true已在用，false未用
public static bool FileHasOpened(string fileFullName)
{
    bool lOpened = false;
    bool lRetry = true;
    do
    {
        if (!CheckFilesState(fileFullName))
        {
            if (DialogResult.Cancel == MessageBox.Show("文件只读或已经被打开，请处理后再操作！", "系统错误！", MessageBoxButtons.RetryCancel, MessageBoxIcon.Warning))
            {
                lRetry = false;
                lOpened = true;
            }
        }
        else
            lRetry = false;
    } while (lRetry);
    return lOpened;
}
#endregion